I've been brewing 6 batches of Ale and I've had problems with sweetness and banana like aroma and taste (esters probably). I think the problem is the fermentation temperature. My fermentation bucket sits in a room with a temperature ranging from 20 to 27 celsius (68-81 fahrenheit). The only brew that tasted "right" was a stout but the roasted barley might have just masked the sweetness. The sweetness is present after few days of fermentation and then gets stronger. I have used US-05, WY 1056 and WY 1272 yeasts.

I was thinking of making a fermentation chamber from a larger bucket (than the fermentation bucket) with insulation of the outside. The temperature would be controlled with adding cold water to the bucket and removing warm water. Do you think this would do the job? If I have understood correctly the first days of the fermentation are the most important temperature wise.

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ScottJun 6 '13 at 15:03

I will get back to you after the next batch which will be fermentented in a lower temperature!
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anssiasJun 12 '13 at 10:43

3 Answers
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It's certainly possible that the banana esters are due to warm fermentation temperature.

After sanitation, I'd argue that the most important step in brewing is fermentation temperature. You want both the correct temperature for your yeast (each yeast varies so check the manufacturer), and a consistent temperature. The method you mentioned helps primarily with regulating temperature fluctuation, but it can be helpful in maintining the correct temperature, too, if you're diligent.

A fellow brewer did an experiment with another yeast, varying multiple batches with the same yeast by a few temperatures and found very noticeable differences in the aromas produced. So I think temperature is the answer, although it could be too warm or too cool - you'd have to experiment to find out.
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paulJun 17 '13 at 20:11

I started brewing extracts a couple of months ago and I started to do the "swamp cooler" method which sounds similar to that which you have postulated. The only difference is that I never replace the water.

I would recommend using a outer bucket filled with water up to the level of the fermenting wort, and make sure the bucket has a large enough diameter so that you can add frozen water bottles to it. I do this every hour on hot days (like yesterday!).

Get a thermometer and measure the ambient temperature of the room the fermenting wort is, and then measure the water in the outer container, and note the difference. If the water is at 75*F, you may not have to add water bottles, although I do during the first 4 days of fermenting because supposedly the exothermic reaction adds 10*F, so I add enough frozen water bottles during that time to knock it down to 65*F.

Also, make sure the outer container is not to tall. Place a black t-shirt over the fermenting-bucket/carboy and then place a fan at the t-shirt (the shirt wicks up water, the fan evaporates the water, leaving you another 10-15*F to not worry about).

The "Swamp Cooler" mentioned above is the best way to cheaply/easily regulate the carboy's temp. I would just add that you need to stick a thermometer strip onto the carboy right above the water line. Then, add enough frozen bottles to keep the carboy thermometer strip reading a constant 65F for most ales.
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GrahamJun 4 '13 at 13:23

@graham Do you recommend the 65*F due to the exothermic addition of 10*F?
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Matthew MoisenJun 4 '13 at 17:17

No, I mean that the carboy itself and the fermenting wort should be right at 65F. By using a stick-on thermometer (or better yet, a probe thermometer in the liquid itself, like a ThermoWell), you eliminate the need to care about the temp difference in the surrounding environment. Different kinds of fermentations throw different amounts of heat, (as low as 2-3 degrees F, or as high as 14-15), so its better to just measure the temp of the wort than to try to plan how cold to get the surrounding liquid or air.
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GrahamJun 5 '13 at 12:06

I agree with others; I think your fluctuating temperature is the likely cause. I have never tried the swamp method but I am about to convert a refrigerator into a fermentation chamber.

I have a temperature control unit I picked up on ebay from someone in Hong Kong - the unit name escapes me at the moment. I am going to by-pass the thermostat on the fridge and hook up the temperature control to activate the compressor when too warm and a low wattage light bulb, that I will fix to the bottom of the fridge, when too cool to provide heat.

I am hoping to source a second-hand fridge this week, so I might be able to get started on this at the weekend.

If you Google 'fridge fermentation chamber' you can find quite a few links to blogs and forums on this.